The spine is formed of superposed vertebrae, normally aligned along a vertebral axis, from the lumbar vertebrae to the cervical vertebrae, each having an anterior part called the vertebral body, and a posterior part called the vertebral arch, or neural arch, the anterior and posterior parts enclosing the vertebral foramen. Each vertebral arch is formed by a pair of pedicles and a pair of laminae, with transverse processes and/or a spinous process (or neural spine) projecting therefrom. The transverse processes and the spinous process project opposite to the vertebral foramen.
When the vertebrae are articulated with each other, the vertebral bodies form a strong pillar for the support of the head and trunk. In between every pair of vertebral bodies, there is an intervertebral disc.
When the spine of a person has abnormal curvature (e.g. scoliosis) or other deficiencies (e.g. a damaged intervertebral disc), the vertebrae are typically too close together, too far apart or otherwise misaligned, and there is a need to stabilize the vertebrae in a correct position relative to one another. Mainly, there is either a need to compress the vertebrae, i.e. to bring and hold them closer together, or a need to distract the vertebrae, i.e. to move and keep them away from each other.
Devices known in the art for holding vertebrae relative to one another typically include one or more support members such as rods that are attached to the vertebrae by means of pedicle screws, hooks, or flexible ligatures.
Pedicle screws typically have a tulip-shaped head to which the rod is attached. Examples of a pedicle screw are given in patent document US2011/0040328A1. Pedicle screws are screwed into the pedicles of the vertebrae for forming fixing points on the vertebrae. However, in some cases the pedicles are small and/or deteriorated, e.g. due to osteoporosis, can be damaged or, more generally, do not provide sufficient purchase to hold the screw through time.
Patent document EP2052689A1 discloses examples of devices using a flexible ligature. In such devices, a connection member, or connector, is fixed to the rod and a flexible elongate ligature connects the connector to at least one rib and/or transverse process and/or lamina, the connector maintaining traction applied to the ligature. However, ligature attachment sometimes allows a certain amount of relative movement between the connector and the vertebra, which can be a drawback in some cases.
Patent document WO2012/025585 discloses a device using both a hook and a flexible ligature to connect a support member to one location in a bony structure.
While known devices have proven effective, further improvements would be beneficial.